The term sneaky pete originally applied to a one piece house cue that was cut into two pieces for easier transport and concealment of its identity. This was during an era when most players used house cues (Brunswick Titlists). It was unusual for a casual player to own a cue. So, if you walked with a leather satchel carrying your own cue (Willie Hoppe or Rambow), you were considered a really good player, like Fast Eddie from The Hustler.
Nowadays, its simply a encompassing marketing term used to stroke your ego, and romanticize the imagined past. In the AZ forsale section, I've seen the term sneaky pete used to refer to any plain basic cues, or a lightly adorned cue as a fancy sneaky pete.